Re: chilled hopback... I think the intent when using is to run the HOT wort thru the hops to allow the aroma+flavor to pick up from the hops. Then IMMEDIATELY chill on the outlet to lock this into the wort.
It would work better hotter than cold. If you intend to run it thru cold, you could just dry hop.
So i'm not sure you're going to get your intended utilization. you would loose some during ferment anyway so you want as much as possible in there.